1. Field of the Invention
The present invention relates to a master carrier for magnetic transfer, which has a projection pattern for digital information transfer to magnetic recording medium, and in particular to the projection pattern of such a master carrier.
2. Description of the Related Art
With the recent increase in information data in the art of magnetic recording media, generally desired are inexpensive, mass-storable and rapid-accessible media capable of recording many informations and preferably capable of reading out the necessary site within a short period of time. For example, high-density magnetic disc media are known that are used in hard disc devices and floppy (registered trade mark) disc devices. A tracking servo technique plays a significant role in realizing the mass storability of such media, which is for driving a magnetic head to accurately scan even narrow tracks and to reproduce signals as a high S/N ratio. Discs are preformatted to record tracking servo signals, address information signals and reproduction clock signals at predetermined intervals in one circle of each disc, and a recording head is so designed that it can read these preformatted signals and can therefore correct its own position to accurately run on the track of each disc.
In general, servo signals (servo patterns) include a preamble (synchronization signal), a gray code (track number signal) and a burst signal (head positioning signal) that are formed in that order from the top of a servo frame, and a data region follows their region. The burst signal has a part where it is recorded as shifted by ½ track width from the track center line, and the other servo signals are recorded on the track center line to a whole track pitch width. The data region is narrower than the recording width of servo signals, and a guard band part where no signal is recorded is formed in the area adjacent to the outer and inner tracks.
At present, every disc is preformatted one by one by recording the signals one by one thereon, using a dedicated servo recording device. For example, the servo recording device is equipped with a magnetic head that has a head width of about 75% of the track pitch. First, the magnetic head is kept in adjacent to a disc, and the disc is rotated once in that condition to thereby write a pattern thereon that corresponds to the outer ½ track width. Next, the magnetic head is moved inside by a half track pitch width of the disc, and a pattern that corresponds to the inner ½ track width is written on the disc in the next rotation thereof. In that manner, the one-track signal is formed on the disc.
The servo recording device is expensive, and takes a lot of time for preformatting discs with it. Therefore, the preformatting process takes a major part of the production cost of discs, and it is desired to reduce the cost.
Accordingly, a method of preformatting discs in a mode of magnetic transfer has been proposed, in place of preformatting them one by one for one by one track thereon. For example, U.S. Pat. No. 6,347,016 discloses magnetic transfer techniques. For magnetic transfer, a master carrier is prepared, which has a projection pattern corresponding to the information to be transferred onto magnetic disc media such as slave media, i.e., magnetic recording media. The master carrier is kept in intimate contact with a slave medium and a magnetic field for transfer recording is applied to them, whereby the magnetic pattern corresponding to the information (e.g., servo signals) that the projection pattern of the master carrier carries is recorded onto the slave medium. The process enables static recording, not changing the relative position between the master carrier and the slave medium. According to the process, therefore, accurate recording of preformat data on slave media is possible, and the time necessary for the recording may be extremely short.
For improving the transfer quality in the above-mentioned magnetic transfer process, it is important to solve the problem of how to keep the master carrier and the slave medium in intimate contact with no gap between them. In other words, if they are not kept in good intimate contact with each other, then no magnetic transfer may occur in some region. The magnetic transfer failure will cause signal failure of the magnetic information transferred onto the slave medium, and the transferred signal quality is thereby lowered, and when the recorded signal is a servo signal, then it could not satisfactorily attain its tracking function and the signal-reading reliability thereof may therefore lower.
FIG. 5 is a plan view for explaining the positional relationship between a servo pattern region and a data region of a magnetic transfer master carrier. In the drawing, M5 is a magnetic transfer master carrier; S1, S2, S3, S4, S5, . . . each are a servo pattern region; and D1, D2, D3, D4, D5, . . . each are a data region. In the drawing, the regions are drawn wide for better visibility. In fact, however, one region has a center angle of about 2 degrees. Further, the servo pattern region S1, . . . is drawn wider in some degree than the data region D1, . . . In fact, however, the difference between them is much larger than that in the drawing. FIG. 6, FIG. 7, . . . that are described below each show the cross-sectional view of FIG. 5 in the T1 direction thereof.
FIG. 6 is a cross-sectional view showing a condition of magnetic transfer onto a slave medium from a conventional magnetic transfer master carrier. (a) is the master form before transfer; and (b) is the master form during transfer.
In the drawing, M6 is a conventional magnetic transfer master carrier; S is a slave medium; S1 and S2 each are a serve pattern region; and D1 and D2 each are a data region. As seen in the drawing, the conventional magnetic transfer master carrier does not have a projection in the data region D1, D2, and therefore an air layer L1 is between the carrier M6 and the slave medium S.
In the magnetic transfer process illustrated, the master carrier and the slave medium are kept in contact with each other for preformat signal formation. As in FIG. 6(a), the magnetic transfer master carrier M6 is kept in contact with the slave medium S, and then the gap between them is degassed to be in the condition as in FIG. 6(b) in which an external pressure P is applied to the master carrier M6 and only the preformat signal projections are kept in contact with the slave medium. In this, therefore, the preformat signal projections undergo high-order distortion while they are in contact with the slave medium. Specifically, the sites m2 and m4 with no projection formed therein are warped and deformed, and therefore, the sites m1 and m3 with projections formed therein are influenced by the deformed sites, and are therefore deformed as in the drawing. As a result, accurate magnetic transfer onto the slave medium becomes impossible owing to the high-order distortion of the preformat signal projections, and the quality of the transferred slave medium is therefore low. In addition, the projections of the servo pattern region are also gradually changed and collapsed, and the material of the curved site is fatigued, and to that effect, the durability of the master carrier is problematic.
When the master carrier M6 is repeatedly brought into contact with the slave medium S, then the lubricant in the slave medium S and the contaminant in air may adhere to the master carrier M6. The lubricant and the contaminant thus having adhered thereto are difficult to remove from the master carrier, and also to that effect, the master carrier could not ensure good durability.
On the other hand, a different type of master carrier that does not form an air layer between it and a slave medium is known, for example, as in JP-A2001-126247 and JP-A11-273070. The master carrier of the type is so designed that the data region thereof is formed to the same height as that of the servo pattern region thereof in producing it, and a magnetic layer is embedded in only the servo pattern region, and, as a result, the height of the servo pattern region is made the same as that of the data region.
FIG. 7 is a cross-sectional view of a magnetic transfer master carrier common to JP-A 2001-126247 and JP-A 11-273070.
In the drawing, 50 is a servo pattern region of a magnetic transfer master carrier; 51 is a non-magnetic support; and 52 is a ferromagnetic thin film.
For producing the master carrier, a resist is applied to the surface of the non-magnetic support 51, exposed to light, developed and etched to form a groove pattern on the non-magnetic support 51, and a ferromagnetic thin film 52 is formed on it. Next, the remaining resist and the unnecessary ferromagnetic thin film are removed to obtain the servo pattern region 50 as in FIG. 7(a).
Specifically, the magnetic transfer master carrier 50 is so designed that its surface is flat and a ferromagnetic layer is embedded in it. When the master carrier is kept in contact with a slave medium on the side of the ferromagnetic layer thereof, then the two can be kept in intimate contact with each other with no gap between them, and ensure good magnetic transfer between them. Since the master carrier of the type has no projection on its surface, its durability is good and its life is long.
JP-A 2001-126247 and JP-A 11-273070 may clarify the constitution of the servo pattern region of the master carrier disclosed therein, but have no description relating to the data region thereof. From the production method for the master carrier, it may be presumed that the non-magnetic support 51 itself may serve as the data region of the master carrier. If so, the magnetic transfer master carrier having the servo pattern region and the data region presumed from Patent References 1 and 2 will be as in FIG. 7(b).
In FIG. 7 (b), M7 is a magnetic transfer master carrier comprising a servo pattern region and a data region; 51 is a non-magnetic support; 52 is a ferromagnetic thin film; S is a servo pattern region 50; and D is a data region. When the thickness of the master carrier in the servo pattern region is represented by d1 and those in the data region is represented by d2, then d1=d2.
The surface of the magnetic transfer master carrier M7 is flat as illustrated. Therefore, when this is kept in intimate contact with a slave medium, then no air layer is formed between the data region D and the slave medium. In that condition, this is free from high-order distortion that is caused by only the contact of the preformat signal projections with the slave medium as in FIG. 6. Accordingly, the master carrier of this type may ensure accurate magnetic transfer onto slave media, therefore having the advantages of good durability and long life.
However, the magnetic transfer master carrier M7 of FIG. 7 does not have a projection pattern in the servo pattern region thereof, and therefore the boundary between the magnetic region and the non-magnetic region is difficult to clarify. In particular, when magnetic powder adheres to the flat non-magnetic region, then this will rather interfere with accurate magnetic transfer onto slave media. Another problem with the master carrier M7 is that it requires a step of embedding the magnetic region 52 into the non-magnetic region 51.
Another type of magnetic transfer master carrier as in FIG. 8 may solve the problem. FIG. 8 is a cross-sectional view showing a condition of magnetic transfer onto a slave medium from a magnetic transfer master carrier. (a) is the master form before transfer; and (b) is the master form during transfer.
In the drawing, M8 is a conventional magnetic transfer master carrier; S is a slave medium; S1 and S2 each are a serve pattern region; and D1 and D2 each are a data region.
As seen in the drawing, the magnetic transfer master carrier M8 is characterized in that a projection T1, T2 is formed to be the entire data region D1, D2 thereof, and its height is the same as that of the projections in the servo pattern region S1, S2. Accordingly, when the master carrier of the type is attached to a slave medium, then an air layer like L1 as in FIG. 6(a) is not formed between it and the slave medium S attached thereto, like in the case of FIG. 7. Therefore, even when a pressure P is applied to the master carrier during magnetic transfer with it as in FIG. 6(b), there occurs no high-order distortion that may be caused by the contact of only the preformat signal projections of a master carrier to the adjacent slave medium. As a result, the master carrier of the type ensures accurate magnetic transfer with it, and has the advantages of good durability and long life.
However, the projection in the data region of the magnetic transfer master carrier of FIG. 8 is formed of the same magnetic support as in the servo pattern region thereof, and therefore, the master carrier of the type is unfavorable since the data region thereof may also undergo magnetic transfer at the same time when the servo pattern thereof is subjected to magnetic transfer onto slave media.
Accordingly, the master carrier must be specifically so designed that the data region thereof does not undergo magnetic transfer while the serve pattern thereof is subjected to magnetic transfer onto slave media. For it, for example, the servo pattern region and the data region of one and the same master carrier may be so synchronized that the master carrier may receive a magnetic field only in the servo pattern region thereof but not in the data region thereof while it is driven for magnetic transfer onto slave media. However, controlling the master carrier to that effect is complicated and troublesome.
Common to the two magnetic transfer master carriers of FIG. 7 and FIG. 8, another problem is that there exists no groove passing in the radial direction, in the boundary between the projections-having servo pattern region and the data region of the two.
The master carrier of the type as above, in which the projection of the data region is formed of the same non-magnetic support as in the servo pattern region and has the same height as that of the servo pattern region, has the advantage of good intimate contact with a slave medium with no gap between them, but naturally, it does not have any other function, such as a cleaning function of absorbing a lubricant released from a slave medium attached thereto.
Even when a flat master carrier is attached to a flat slave medium, the two could not always be in completely intimate contact with each other in the entire surface thereof, and air bubble islands may be formed in the area where air discharge by suction is delayed, and if so, they may rather cause magnetic transfer failure. The magnetic transfer master carriers of FIG. 7 and FIG. 8 could not repel such air bubbles.